<template>
    <div class="pagination">
        <!-- <h1>{{ startAndEnd }}</h1> -->
        <button @click="$emit('currentPage', pageNo - 1)" :disabled="pageNo==1">上一页</button>
        <button v-if="startAndEnd.start > 1" @click="$emit('currentPage', 1)">1</button>
        <button v-if="startAndEnd.start > 2">.....</button>

        <!-- 中间连续页码的地方:v-for、数组、对象、数字、字符串 -->
        <button v-for="page in startAndEnd.end" :key="page" v-if="page >= startAndEnd.start"
            @click="$emit('currentPage', page)" :class="{ active: pageNo == page }">{{ page }}</button>

        <button v-if="startAndEnd.end < totalPage - 1">......</button>
        <button v-if="startAndEnd.end < totalPage" @click="$emit('currentPage', totalPage)">{{ totalPage }}</button>

        <button @click="$emit('currentPage', pageNo + 1)" :disabled="pageNo == totalPage">下一页</button>

        <button style="margin-left: 30px">共 {{ total }} 条</button>
    </div>
</template>
  
<script>
export default {
    name: "Pagination",
    // 总业数 页面大小 当前页面 连续展示的分页个数
    props: ["total", "pageSize", "pageNo", "pagerCount"],
    computed: {
        //分页器一共多少页【总条数/每页展示条数】
        totalPage() {
            //向上取整数
            return Math.ceil(this.total / this.pageSize);
        },
        //底下的代码是整个分页器最重要的地方[算出连续五个数字、开头、结尾]
        startAndEnd() {
            //算出连续页码:开始与结束这两个数字
            let start = 0,
                end = 0;
            const { totalPage, pagerCount, pageNo } = this;
            //特殊情况:总共页数小于连续页码数
            if (totalPage < pagerCount) {
                start = 1;
                end = totalPage;
            } else {
                //正常情况：分页器总页数大于连续页码数
                start = pageNo - parseInt(pagerCount / 2);
                end = pageNo + parseInt(pagerCount / 2);
                //约束start|end在合理范围之内
                //约束头部
                if (start < 1) {
                    start = 1;
                    end = pagerCount;
                }
                //约束尾部
                if (end > totalPage) {
                    end = totalPage;
                    start = totalPage - pagerCount + 1;
                }
            }
            return { start, end };
        },
    },
};
</script>
  
<style lang="less" scoped>
.pagination {
    button {
        margin: 0 5px;
        background-color: #f4f4f5;
        color: #606266;
        outline: none;
        border-radius: 2px;
        padding: 0 4px;
        vertical-align: top;
        display: inline-block;
        font-size: 13px;
        min-width: 35.5px;
        height: 28px;
        line-height: 28px;
        cursor: pointer;
        box-sizing: border-box;
        text-align: center;
        border: 0;

        &[disabled] {
            color: #c0c4cc;
            cursor: not-allowed;
        }

        &.active {
            cursor: not-allowed;
            background-color: #409eff;
            color: #fff;
        }
    }
}
</style>